Chronic wasting disease a growing threat to deer herds

When the province of Saskatchewan announced last spring a deer had tested positive for chronic wasting disease just a few miles into Canada north of Portal, N.D., officials for the North Dakota Game and Fish Department braced themselves for the p...

Written By: Brad Dokken
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Jan 27th 2019 - 6am.

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This emaciated deer in Iowa County, Wis., was later confirmed to have CWD. Most animals that carry the disease look healthy. It's only in the final stages where they become sickly looking. Wisconsin DNR photo.

When the province of Saskatchewan announced last spring a deer had tested positive for chronic wasting disease just a few miles into Canada north of Portal, N.D., officials for the North Dakota Game and Fish Department braced themselves for the possibility of a similar finding in the northwest part of the state, where CWD previously hadn't been found.

That possibility became reality in December, when Game and Fish confirmed a mule deer buck shot in November in Divide County in hunting unit 3A1 tested positive for CWD. The news marked the first time the neurological disease fatal to cervids-deer, elk and moose-had been found outside unit 3F2 in southwest North Dakota.

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Disappointing, but not surprising, is how Game and Fish Wildlife Chief Jeb Williams described the finding in a December interview.

First detected in a captive mule deer at a Colorado research facility in 1967, CWD falls into a category of diseases known as transmissible spongiform encephalopathies-including mad cow disease in cattle, scrapie in sheep and goats and Creutzfeldt-Jakob disease in humans-that in lay terms degenerate the brain to the point where it resembles a sponge.

CWD hasn't been known to infect humans, but consuming meat from infected animals isn't advised, the Centers for Disease Control and Prevention says.

Unlike wildlife diseases such as bovine tuberculosis, which are caused by living organisms and eventually run their course if caught and controlled early enough, the CWD pathogen is there to stay once it's on the landscape. CWD is caused by abnormal proteins called prions, which readily spread from infected to healthy animals through feces, saliva and other bodily fluids, carcasses from dead deer and numerous other transmission agents.

Infected deer shed those prions, which then can contaminate both soil and plants and are all but impossible to destroy, said Dr. Charlie Bahnson, wildlife veterinarian for the North Dakota Game and Fish Department in Bismarck.

"There was a pretty good study from 2004 where under an experimental setting, they took an infected carcass, let it decompose in a pen and two years later put a healthy deer just in that pen, so the carcass was long gone," Bahnson said. "That was still sufficient for that healthy deer to then become infected."

As the University of Utah Learn Genetics Science Center says on its website, "you can't kill what isn't alive."

So it is with the prions that cause CWD.

Paper airplane analogy

Because a prion isn't a fungus, virus or bacteria, the concept can be difficult for people to wrap their minds around. Think of it like a paper airplane, Bahnson says, describing an analogy he recently came across in his research on the disease.

"Your body has lots of these normal proteins or normal prions, but what's really important with those is how they're actually structured-or how they're folded, is the terminology," Bahnson said. "So, if you had this protein, which is a piece of paper and it's folded into a paper airplane, then that's a functional way to send a message and accomplish a task.

"Whereas, if you took that same piece of paper and just balled it up into a crumpled ball, then all of a sudden it loses its function; it can't fly, it can't be used to send a message. And these prions are kind of the same way."

In the case of a deer infected with CWD, those dysfunctional prions-the protein equivalent of balled-up pieces of paper-disrupt the nervous system and the animals eventually die.

That can take 18 to 20 months from the time of exposure, and a deer can appear healthy until shortly before death. None of the 14 deer confirmed with CWD in North Dakota since 2009-including the buck in 3A1 and two other new positives in 3F2-showed clinical signs of the disease, Bahnson says.

That's why testing is so important.

"One pretty common perception is that there's this deer out there, it looks perfectly healthy, so it must be free of CWD," he said. "But really, it will only become apparent, and the deer will only look sick toward the end of that 18 or 20 months. For most of that time, it will be shedding those prions and look like a healthy deer but it is truly infected.

"So, that's also one of the challenges of this disease."

Taking steps

For wildlife managers, that leaves few options for controlling CWD.

Prevention is the first line of defense and includes measures such as restricting the import of deer carcasses from other states and provinces, either entirely-as Minnesota does-or from infected areas, as North Dakota does.

In both instances, hunters can transport quartered, deboned or processed meat from the animals they shoot, but the brain tissue and spinal column must remain where the animal was shot.

When CWD is found, agencies often turn to more restrictive measures, such as baiting or feeding bans to limit deer from congregating, liberal hunting regulations, culling and intensified testing.

Those approaches vary by state, said Lou Cornicelli, wildlife research program manager for the Minnesota Department of Natural Resources in St. Paul.

In Wisconsin, for example, where CWD is widely established, former Gov. Scott Walker in May 2018 signed an emergency rule to restrict carcass movement within the state, only to have the Legislature reverse it in early October.

The DNR in Minnesota can implement such restrictions through its rulemaking authority, Cornicelli said.

"The Minnesota DNR has broad regulatory authority, which we're thankful for," Cornicelli said. "However, not all states do.

"Each state manages its own nonmigratory wildlife populations, and each state has different authorities to how those animals can be regulated."

North Dakota implemented carcass and baiting restrictions in unit 3F2 in southwest North Dakota where CWD first was found, and similar restrictions are on tap for the northwest part of the state after the recent confirmed case in 3A1.

Hunters in North Dakota still can transport whole carcasses from uninfected parts of the state, and baiting outside of infected areas is allowed on private land.

"Our recommendation is going to be to follow the same protocol as in 3F2 as far as baiting bans and transportation restrictions" in northwest North Dakota, Williams said. "It's going to be something we're going to have to look at. We still have a lot of discussion to do on it."

Assessing risks

In Minnesota, the DNR is working to limit the spread of CWD in the southeast part of the state with an aggressive strategy that includes special hunting seasons, intensive mandatory testing and feeding bans. Baiting long has been illegal statewide.

Minnesota as of early January had confirmed more than 30 positive cases of CWD in wild deer, all in the southeast, Cornicelli said.

The DNR has been conducting surveillance around captive deer and elk farms known to have CWD for the past 16 years, Cornicelli said. The first known case of CWD in Minnesota occurred in 2002 at a captive elk farm in Aitkin County.

As of April 2018, CWD had been identified on eight Minnesota deer and elk farms, according to a Minnesota Legislative Auditor report on farmed cervids. Such findings prompt the DNR to implement intensified testing and prevention measures in areas surrounding the positive farms.

The first wild deer to test positive for CWD came from Olmsted County in 2010, within 2 miles of an elk farm that tested positive the previous year.

"The way we do surveillance is what we call risk-based," Cornicelli said. "We can't afford to do surveillance everywhere all the time. So we look at risk, and risk is measured by the disease found in other locations and by symptomatic deer that we see on the landscape or positive captive cervid facilities."

The DNR since 2002 has tested more than 64,000 wild deer for CWD, Cornicelli said. In North Dakota, Game and Fish tested about 1,500 deer this past fall in the western part of the state, Bahnson said.

Hunters drop deer heads at designated collection sites, and Game and Fish staff then remove lymph node samples, which are sent to a federal lab. Testing in North Dakota is voluntary, Bahnson said.

"Our surveillance is kind of two-fold, so we do the widespread hunter-harvested surveillance and then we do targeted surveillance, so any deer that looks sick in the state that the department can get their hands on, we'll go ahead and test," he said. "We really focus that (widespread) surveillance on one-third of the state every year. So, last year, we were in the central third, and this (past) year we were in the western third of the state."

Hope amid gloom

Even with an aggressive strategy, prospects for eliminating CWD from the landscape appear slim, Cornicelli concedes.

"It's looking less likely, given we keep finding positives and start seeing positives spread out a little further," he said.

No doubt, the long-term implications "are very real and very serious," Bahnson said.

"We can live with a low prevalence indefinitely, but what's been shown in other states is once you start to creep up-I hate to throw out a number, but once you get into relatively high prevalence-then all of a sudden you do start to see effects on the population.

"When we find the positive detections, it means we've got to do all we can to try to protect this population for the future."

If the disease becomes rampant, the options become fewer.

"Hunters have to be aware of the rules we've implemented to help keep our deer safe," Cornicelli said. "They're not being implemented to make people's lives difficult. They're implemented because we have real concerns about the disease popping up in another county-pick one."

"If you read some of the stuff coming out of the outdoors literature, they're saying that-and I agree with it," he said.

If there's a bright spot, it's that awareness is increasing.

"I say that in my state," Cornicelli said. "It's maybe too late in others, but I say that in our state as we see more positives or we see more persistent infection, people are going, 'This is really serious.'"